Active network measurement is a way to get information about network connection characteristics for using network resources in a most efficient way. “Active measurement” in this context means network performance measurements based on the injection of additional data packets into the data network. The measurement is then performed by analyzing the basic parameters of such probe samples. The most important parameters hereby are one-way delay (OWD) and inter packet time interval measured in the receiving station (IpIR). This is the time interval between receptions of two consecutive arriving samples. The receiving station takes the time when the probe sample data packets arrive and calculates the inter packet time interval (IpIR). In the following for the long expression “probe sample data packets” the short forms “probe sample packet” or “probe packet” are synonymously used. An example of a “probe sample data packet” is an UDP datagram that contains a time stamp showing the time of the sending station when this datagram has been sent. UDP here stands for the well-known user datagram protocol.
Due to variations in transmission paths and in queuing hold-up, the transmission delays experienced by the different packets can vary considerably in a non-deterministic way. In extreme cases, a packet sent earlier may arrive at a later time than one that was sent later.
There exists in literature a so-called probe rate model (PRM). According to this model, the sender iteratively sends probe sample packets via the network to a receiver. Per iteration the measurement is performed with a different constant bit rate (CBR). Per iteration, the sender sends a so called train of probe samples—certain amount of consecutive probe samples sent with a constant inter packet time interval (IpIS) measured in the sending station. After reception of the train of probe samples, the receiver analyses the received datagrams and their arrival times and makes a suggestion whether the CBR in the last iteration was higher than the available bandwidth or not. If the result shows that CBR is higher—then the receiver generates a new inter-packet time interval that should be used by sender (IpIS) for the next iteration. So, this will be fed back to the sender in a message. The relation between CBR and IpIS is shown in equation (1)
                              CBR          =                      SS            IpIS                          ,                            (        1        )                            where SS is the Segment Size of the UDP packet.        
Measurements according to the PRM model begin with a maximum possible CBR (e.g. with the link data rate at the sender, i.e. probe packets are “pumped” into the data pipe with the minimum possible distance in time) and then iteratively decreased until the receiver assumes, that the CBR of the last iteration was not higher than the available bandwidth on the path between the data sender and data receiver. This is the end point of the measurement phase and the available bandwidth is assumed to be not less than the last used CBR.
The PRM model is described in the following articles:    [1] M. Jain and C. Dovrolis, “End-to-end available bandwidth: measurement methodology, dynamics, and relation with TCP throughput,” IEEEACM Trans. Netw., vol. 11, no. 4, pp. 537-549, August 2003.    [2] J. Sommers, P. Barford, and W. Willinger, “A Proposed Framework for Calibration of Available Bandwidth Estimation Tools,” in 11th IEEE Symposium on Computers and Communications, 2006. ISCC '06. Proceedings, 2006, pp. 709-718.